This invention is directed to electronic musical instruments and more particularly to an improved envelope generating circuit for controlling the attack time of musical tones generated by an electronic organ.
In electronic musical instruments, it is advantageous to provide an arrangement for controlling the tone envelope, i.e., the rate of attack and decay of the tone signal to avoid transients which introduce objectionable noise and also to achieve various desirable special effects. For example, in electronic organs a keying signal from a playing key of the organ manual is modulated by a defined envelope signal such that the rate of attack and decay of the keying signal is controlled.
The rate of attack and decay for an applied signal in an electronic organ is typically controlled by the charging and discharging of a capacitor via one or more resistors with the amount of resistance in the charging and discharging paths determining the attack and decay rate of the envelope applied to the music signal. Accordingly, the volume increase and decrease in organs incorporating such envelope generating circuits have an exponentially increasing attack and an exponentially decreasing decay. To be musically correct, the attack or increase in volume of a musical tone as it is played should be in equal numbers of decibels for equal increments of time. Although an exponential increase is a good approximation, it does not achieve the musically correct rate.